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Lung Volume and Capacity

Anisha ValliLeave a comment

Spirometer: measures an individual’s pulmonary functio

  • Allows you to record lung volume measurements
    – Generates a graph (spirogram) to analyze the efficiency of an individual’s lung function.
  • Here, we analyze the spirogram of an average adult male
    y-axis = volume (liters) → spirograms record air volume (between 0 – 6 liters)
    x-axis = time (seconds) → spirograms record over time.

Key Values and Spirogram Analysis:

Tidal volume (TV):

Volume of air inspired during quiet breathing → 0.5 liters

Inspiratory reserve volume (IRV):

Forced inhalation → 3.0 liters

Maximal (peak) inspiration

= 6.0 liters lung volume

Expiratory reserve volume (ERV):

The volume of forceful exhalation → 1.0 liter

Maximal expiration

= 1.5 liters lung volume

Residual volume (RV):

The volume of air still in the lungs after maximal expiration

Lung capacity = sum of two or more lung volumes

Vital capacity (VC): The difference between maximal inspiration and maximal expiration.

VC = TV + IRV + ERV

Total lung capacity (TLC): the total volume of air that the lungs can hold.

TLC = VC + RV

Inspiratory capacity (IC): the maximum volume of air that the lungs can inspire.

IC = IRV +TV

Functional residual capacity (FRC): the volume that remains in the lungs after a single quiet breath.

FRC = ERV + RV

Pulmonary Ventilation and Alveolar Gas Exchange:

Conducting portion:

Trachea → left, right bronchi → terminal bronchioles

  • Only air conduits, do not participate in gas exchange.
  • This is the anatomic dead space*
  • Gas exchange primarily occurs in the respiratory bronchioles and alveoli.

Healthy Lungs vs. Emphysema

Healthy lungs:

Physiologic dead space = anatomic dead space.

Emphysema:

Physiological dead space > anatomic dead space.

  • Lungs lose elasticity → insufficient recoil → air is trapped in lungs, unable to be exhaled
  • Air now part of the physiologic dead space *
  • Increase in RV (volume of air remaining in the lungs after maximal expiration)
  • Decrease in vital capacity.
  • Individuals have “barrel chest” → accommodates increased RV

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